Update coverage test dep.

Author: ionelmc

tox.ini

@@ -28,7 +28,7 @@ setenv =
     coverage45: _DEP_COVERAGE=coverage==4.5.4
     coverage50: _DEP_COVERAGE=coverage==5.0.4
     coverage51: _DEP_COVERAGE=coverage==5.1
-    coverage52: _DEP_COVERAGE=coverage==5.2
+    coverage52: _DEP_COVERAGE=coverage==5.2.1
     # For testing against a coverage.py working tree.
     coveragedev: _DEP_COVERAGE=-e{env:COVERAGE_HOME}
 passenv =